In the field of intraocular or ophthalmic surgery, as well as in many other technical disciplines, there is a great need for an aspiration or suction system in which the vacuum or negative pressure source can be highly controlled. In ophthalmic surgery, for example, many phacoemulsification instruments use suction to aspirate the emulsified tissue away from the operative site or to allow the surgeon to "grab onto" pieces of cut tissue for manipulation within the surgical field. And, in an ophthalmic vitrectomy operation, many cutting instruments draw the tissue into the cutting edges by use of suction. In fact, the tissue removal rate or fluid flow rate is effectively controlled by the suction effect which is related directly to the negative pressure level. Thus, controlling the negative pressure level to a fine degree is highly desirable to provide the surgeon with a concomitant degree of control of the tissue removal process.
However, prior art suction devices are generally deficient in their poor control of the vacuum level or in their reliance on either an outside vacuum source or a pressurized air source. Many systems employ a pressure delivery tank in which the vacuum level is controlled by selective connection to a lower pressure source. These types of systems are characteristically under-damped pressure oscillators, in that the negative pressure level often swings wildly about the desired and often changing vacuum level. Also, the large volume of most systems causes a delay in their response, which may lead to poor user control and over-shooting of the desired vacuum level.
Many prior art systems use peristaltic pumps or diaphragm pumps to generate the desired vacuum. Examples of such systems are disclosed in U.S. Pat. Nos. 4,180,074, 3,920,014 and 4,168,707. These pump systems are sometimes noisy and are slow to generate the desired vacuum level. Further, it is desirable to have a fast response time for changes in the desired vacuum levels which is difficult to obtain with the use of a peristaltic type pump vacuum system. Such peristaltic pump systems can regulate the fluid flow out of the operative site but cannot control the vacuum level. Such pumps work by pulling the fluid versus controlling the negative pressure level. Further, the working characteristics of a peristaltic pump require use with specific tubings having a known durometer. Over time, the tubing becomes hard thereby changing the operating characteristics of the pump and the reliability of the peristaltic pump system. Furthermore, if a blockage of the aspiration needle of the surgical handpiece occurs, the peristaltic pump keeps trying to pull fluid out of the operative site thereby creating an uncontrolled vacuum rise in the tubing. Upon removal of the blockage, an aspiration surge occurs which can aspirate unintended material out of the operative site possibly causing irreparable damage to the patient's eye.
Various other prior art patents create a vacuum by use of a regulated fluid pressure which is fed through a linear solenoid valve to a venturi-type pressure vacuum converter as is shown in U.S. Pat. Nos. 4,838,281, 4,770,654, 4,810,242 and 4,706,687. The resulting vacuum is proportional to the flow through the solenoid valve and thus to a function of the current through the solenoid. However, in such vacuum systems, the regulated fluid pressure is generated by an outside air supply such as a compressor. In such cases, the compressed air is fed into the microsurgical system under pressure to the air to vacuum converter such as a venturi pump.
This technique for generating a vacuum is wasteful because it requires high rates of air flow to create the vacuum or negative pressure. And, typically the compressor is located externally from the operating area where the surgical procedure is being performed. This would also produce an additional energy waste because the compressor has to work harder to pump the compressed air through the long lengths of tubing to bring the compressed air to the operative site.
Microsurgical devices that depend on an external air pressure source to generate a vacuum are only as reliable as the external air pressure source. Such surgical devices can obviously only operate where such external air pressure sources are available and in good working order. And, while many hospitals in the United States have such external air pressure sources, individual clinics or physicians' offices may not. Further, in many foreign countries low and/or unregulated air pressure sources can disrupt the operation of such microsurgical devices.